I think you will find that it does extend well to other parts of your code. Code that is idempotent allows you to reason much more effectively about what it will do. It always does the same thing and does not introduce side effects. It also allows you to test it much more easily. In fact, doing computations is one of the places where being idempotent will really clean up your code.

It may seem like a new fangled idea, but actually it has been around for quite a long time. It's just that it didn't really get out of academia and the few shops doing functional programming until lately.